“It’s one of the best Park Avenue buildings, built by one of the best architects in the East 70s, which is the best location,” said Brown Harris Stevens’ John Burger, who brokered the last sale in the building, across the hall from the Nemazee’s apartment, and who currently has an eighth-floor listing for $11 million. “You know there are people who will or won’t go to the 60s, and people who won’t go to Carnegie Hill, but no one won’t go to the 70s.”

“The thing that pushes it up in value is the high floor,” Ms. Steinberg said. “There are other duplexes in that building, but not as high up.”

A broker familiar with the apartment said a 2009 government appraisal caused every agent to balk at the idea of a sub-$20 million estimate (the appraisal pegged the value in the high teens).

“If you took a logical approach and the value was a fact-based assessment, the asking price should probably be at $28 million,” the broker, who wished to remain anonymous, told The Observer by phone on Monday morning. “However, in an environment where different firms are giving different presentations for the client, it is in the broker’s best interests to give a higher value in order to flatter the client.”

The broker noted that the government has “a fiduciary duty to achieve the highest price for the property. If one firm gives a presentation suggesting the value at $25 million or $26 million, while another suggests a $29 million value, the government is going to have to have a very good reason before dismissing the $29 million option.”

Ms. Steinberg, who worked with Nemazee on the sale of his late mother’s estate and is familiar with the apartment, agreed with the $28 million estimated asking price. “I think that’s totally, totally fair. It could even go over $30 million, though it’s unlikely.”

But, with 770 Park being among the good buildings, and the apartment being on the larger side, it wouldn’t be surprising.

Last month, David Winter, scion of a family-run real estate concern, purchased a six-bedroom simplex at 778 Park Avenue for $26 million without the apartment even going on the market. “It becomes very subjective,” Ms. Steinberg said. “The apartment wasn’t unique, but it had six bedrooms and that’s very rare. There are only a handful of buildings that have six bedrooms, including 778 Park Avenue and 820 Fifth Avenue.”

“There’s an old-school popularity with those buildings,” Brown Harris Stevens’ townhouse topman Sami Hassoumi said with a sigh. “How would I call it–tradition, I suppose. There is a category of buyers who only go in the direction of old-line co-ops.”

Jonathan Miller, president and CEO of appraisal firm Miller Samuel and an expert on the New York housing market, low and high, summed it up with a dash of real estate realpolitik. “It’s about the exclusivity and prestige–all that is still alive and well.”

“You’re definitely onto something,” Ms. Lenz told The Observer from the curb outside the Plaza. “There’s no question about it.” The December wind rattled her cell, cutting her off mid-sentence. “Big, well-priced apartments sell quickly.”